Infrapatellar contracture syndrome

Infrapatellar contracture syndrome, or patella infera, is a more advanced form of arthrofibrosis.

First published in 2006, and reviewed August 2023 by Dr Sheila Strover (Clinical Editor)

Infrapatellar contracture can occur either in an isolated form - meaning that it affects just the patellofemoral joint – or in a more extensive form in that it also involves the entire knee joint, where it affects flexion and extension of the knee as well.

For the purposes of the discussion I will just limit the discussion to the type of scarring that affects the patellofemoral joint. Where this scarring usually occurs most commonly is in the medial and lateral gutters and directly behind the patellar tendon, sticking the patellar tendon down with scar tissue to the front of the tibia.

 

Effect on Range-of-motion (ROM)

Some patients with this problem will essentially have normal flexion and extension of their knee but they will have increased contact pressures under the patella, or kneecap, and this will subsequently lead to pain and problems with functional activities – particularly things that involve weight-bearing, such as going up and down stairs, or hill climbing – things of that nature. When it becomes more severe, it actually creates a shortening, or contracture of the patellar tendon itself, and that becomes visible on X-rays – you can actually measure that shortening if you compare it from one side to the other, or if you compare it to what a normal relationship of the patellar tendon to the length of the patella would be - and that is known as patella infera or patella baja. That is a more advanced phase of this process.

So early on it just starts as scarring behind the kneecap and around the kneecap, which limits mobility of the kneecap and increases the joint contact pressures, and in the more advanced forms it actually creates shortening of the patellar tendon.

 

There has been quite a bit of work on this – Paulos (ref. 1) was the one who first described this problem, and other people such as Ahmad and Steadman (ref. 2) have done work - we have done work at our clinic looking at the normal excursion of this area. Normally if the knee is placed through a range of motion from flexion to extension, the patellar tendon moves about 1.5-2cm and when someone has developed arthrofibrosis in this region and scarring that normal excursion of the patellar tendon is limited - or eliminated altogether – and that in turn changes the mechanics of the knee, changes the loading pattern on the patella and the groove that the patella rides in (called the trochlea) and that leads to problems with chondromalacia, early cartilage wear and eventually patellofemoral arthritis. So it is very important to recognise this early and treat it appropriately with doing appropriate releases and excision of scar in the pre-tibial recess – it is also called the ‘anterior interval’ of the knee – and also in the peripatellar and the medial and lateral gutters of the knee around the medial and lateral retinacula to ensure that the patella has normal mobility and normal excursion and prevent the more severe types of infrapatellar contracture syndrome.

 

No spontaneous reversal

I personally have seen several cases of severe infrapatellar contracture syndrome and I have not seen it reverse once you start to develop the shortening of the patellar tendon. I have not personally seen it reverse unless there was a significant surgical intervention to lengthen the tendon or to reposition the tubercle -which are very advanced and invasive procedures which we would like to avoid if we can.

 

References

  1. Paulos LE, Rosenberg TD, Drawbert J, Manning J, Abbott P. Infrapatellar contracture syndrome. An unrecognized cause of knee stiffness with patella entrapment and patella infera. Am J Sports Med. 1987 Jul-Aug;15(4):331-41. doi: 10.1177/036354658701500407. PMID: 3661814.
  2. Ahmad CS, Kwak SD, Ateshian GA, Warden WH, Steadman JR, Mow VC. Effects of patellar tendon adhesion to the anterior tibia on knee mechanics. Am J Sports Med. 1998 Sep-Oct;26(5):715-24. doi: 10.1177/03635465980260051901. PMID: 9784821.

 

Author

Dr Peter J Millett

Knee Surgeon

Dr Peter Millett is an orthopaedic surgeon and partner at the internationally renowned Steadman Clinic in Vail, Colorado. ...read more

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